The invention relates to a luminaire comprising:
a hollow reflector having
a plane of symmetry,
a light emission window extending transversely to the plane of symmetry,
reflector side portions on either side of the plane of symmetry; and
means, in the plane of symmetry, for accommodating a tubular electric lamp along the light emission window, which means define a position of an axis of the lamp to be accommodated, in the plane of symmetry,
which reflector side portions each include a first, convex area with an outer edge in the light emission window, and a second concave area which connects to the first, convex area in a line of inflection points, and which has an inner edge close to the axis of the lamp to be accommodated, the line of inflection points being situated at a distance from the light emission window, and the reflector side portions form a lateral screening angle xcex1 of at least 25xc2x0.
Such a luminaire is disclosed in AT-B-386 671.
The known luminaire is intended for use in rooms where display screens are employed.
Therefore, such luminaires are designed such that they do not, or hardly, emit light sideways at an angle of, for example, at least 25xc2x0 with the light emission window, i.e. the so-termed screening angle, in order to make sure that annoying reflections on display screens are avoided. To achieve this, the lamp is arranged so high in the reflector that said lamp is invisible from the screening angle and hence does not emit light in said screening angle. Customarily, such luminaires comprise a concave, for example parabolically curved reflector, which is formed such that also light reflected by the reflector, which light intersects the plane of symmetry of the reflector, is not emitted within the screening angle.
It has been found that small errors in the manufacture of the reflector can lead to deviant shapes, as a result of which parts of the reflector situated near the light emission window do emit light within said screening angle.
In order to increase the permissible variation in shape, and hence preclude this undesirable reflection within the screening angle, the known luminaire in accordance with said AT-B-386 671 comprises a reflector with reflector side portions having a first convex area near the light emission window. The parts of the reflector that are situated near the light emission window thus do not reflect light which, upon reflection, intersects the plane of symmetry at a comparatively small angle with the light emission window; instead they only reflect light which, upon reflection at the outer edge, is emitted at comparatively large angles perpendicularly to the light emission window. The transition from the convex area to the concave area of the reflector side portions, i.e. the line of inflection points, is situated, in the case of the known luminaire, at approximately half the distance from the inner edge to the light emission window. The light that is reflected near the inner edge is emitted perpendicularly to the light emission window.
A drawback of the known luminaire resides in that it produces a comparatively narrow-angle beam, i.e. a beam with a comparatively high luminous flux on the axis and a comparatively rapid reduction of the luminous flux at comparatively small angles with the axis, and in that, if a plurality of luminaires are necessary to illuminate a comparatively large room, the luminaires must be comparatively closely spaced in order to obtain a uniform illumination. As a result, the installation and maintenance costs of the lighting are high.
U.S. Pat. No. 4,403,275 discloses a luminaire comprising a box-shaped housing without a reflector, which luminaire is designed so as to accommodate four juxtaposed, tubular lamps. A smaller luminous flux is obtained by omitting the outermost lamps from said luminaire. Light generated by the innermost lamps may be lost in corners of the housing. This loss is limited by incorporating a screen that is S-shaped in cross-section in the lamp holders intended for the outermost lamps. This luminaire emits light at a very small angle with the light emission window and hence cannot suitably be used in rooms where display screens are employed.
It is an object of the invention to provide a luminaire of the type described in the opening paragraph, which, while the emission of light in the screening angle is precluded, emits light in a uniform manner, also if use is made of a plurality of similar luminaires arranged at comparatively large distances from each other.
In accordance with the invention, this object is achieved in that the distance from the line of inflection points to the light emission window is 0.30 to 0.40 of the distance from the outer edge to the axis of the lamp to be accommodated.
As the line of inflection points is situated comparatively close to the light emission window, the light emission of the luminaire in accordance with the invention, after reflection of the light by a zone situated around the line of inflection points, is such that comparatively much light is sent far away, through the plane of symmetry, at a comparatively small angle with the light emission window. The line of inflection points of the reflector known from said AT-B-386 671 is situated much higher, namely at 0.50 of the distance between the outer edge and the axis of the lamp, which corresponds to 0.54 of the distance from the inner edge to the light emission window.
As a result of the wider spread of the light, which will be shown in the drawings, luminaires in accordance with the invention can be arranged comparatively far apart to obtain a uniform illumination.
The luminaire in accordance with the invention has the advantage that it has a comparatively high flexibility, enabling identical reflector side portions of the reflector to be positioned such that the outer edges are situated at varying distances from each other. As a result, said distance can be adapted to the measurements of modular ceiling systems if the luminaire must be incorporated therein. For example, said distance can be varied between, for example, 125 and 140 mm. By changing the distance between the outer edges, the distance from the outer edge to the axis of the lamp to be accommodated changes too, which axis is defined by the means for accommodating a lamp. Thus, while using an identical reflector side portion, also the position of the line of inflection points changes with respect to the light emission window, expressed as a fraction of the distance from the outer edge to the lamp axis.
Advantageously, the second area is formed, near its inner edge, so as to send the light reflected by it substantially through the plane of symmetry. The light reflected at said location enlarges the luminous flux in directions enclosing an angle with the plane of symmetry, which is not the case in the known luminaire, where light reflected at this location issues to the exterior perpendicularly through the light emission window to contribute to the center of the beam. A uniform illumination is thus obtained at even larger intervals between the luminaires. It is favorable for the second area to be shaped, near its inner edge, such that reflection at the lamp to be accommodated is at least substantially avoided. By virtue thereof, the disturbance of the beam path and loss of light by light absorption by the lamp are precluded.
For the same reason, it is advantageous if the first area is formed such that light reflected by it near the outer edge can be reflected, on the same side of the plane of symmetry, in directions aside. In the known luminaire, at this location the light is emitted to the exterior at right angles to the light emission window so as to contribute to the center of the beam.
In a favorable modification of the luminaire comprising a concave area that extends as far as the inner edge, the second area has a flat zone along the inner edge. By the flat, essentially noncurved zone, comparatively much light is sent obliquely through the plane of symmetry and the light emission window to the exterior, so that, at a uniform or substantially uniform light distribution in the beam, it is possible to employ reflector side portions having a smaller surface area of the second portion. As a result, a saving in material costs can be realized. A further advantage resides in that the reflector side portions can be readily manufactured by roll forming.
The luminaire may comprise a second, substantially identical reflector with second means for accommodating a second lamp, with means for operating the lamps to be accommodated being present between the reflector and the second reflector. A particularly favorable property of the luminaire in accordance with the invention is that, as a result of the shape of the reflector side portions, which shape is also determined by the location of the line of inflection points, there is enough space between the two juxtaposed reflector side portions of a twin or multiple luminaire to accommodate, for example, a ballast or an electronic starter for discharge lamps to be accommodated. As a result, the depth of the luminaire can be reduced, so that less material is necessary and, if the luminaire is to be mounted in a floating ceiling, a smaller space between said floating ceiling and the actual ceiling is sufficient.
The luminaire can be suspended from a ceiling. Said luminaire may be open on the upper side so as to also emit indirect light, or it may be closed. On the other hand, the luminaire may be mounted to or in a ceiling. If desired, the light emission window may be provided with lamellae extending transversely to the plane of symmetry, which lamellae serve to also create a screening angle in the longitudinal direction of the luminaire. The lamellae may be flat or three-dimensional, for example with hollow, such as parabolically curved, side faces. The side faces of flat lamellae may be provided with a relief pattern of, for example, sawtooth-shaped strips, to reflect incident light in a downward direction.
The reflector and, if present, the lamellae may be of a synthetic resin or of a metal, such as aluminum. They may be polish finished, semipolish finished or matt finished. They may alternatively be made of a lacquered material.
The lamellae may have parallel edges in the light emission window and, for example, straight edges within the reflector or, in a suitable case, they may have a concave edge in the light emission window and a convex edge within the reflector. Alternatively, both edges may be convex.
It is favorable for the reflector to be accommodated in a housing which is, for example, diffusely reflecting. In this case, an opening between the inner edges of the reflector is covered, opposite the light emission window, by the housing. And radiation which is diffusely reflected by the housing is uniformly added to the light beam.
The luminaire in accordance with the invention can particularly suitably be used to accommodate a fluorescent lamp having a diameter of, for example, approximately 26 or approximately 16 mm.